Opioid compounds have long been known both for their powerful analgesic properties, and for their strong potential for abuse. While highly effective at controlling pain, opioids can also be addictive. Abuse of opioids, particularly heroin, but also including morphine, codeine, oxycodone, hydromorphone, oxymorphone, and others, is a problem in modern society. Opioid addicts can obtain drugs from a variety of illicit sources. These street drugs are of questionable quality. Therefore, to potential abusers, prescription pharmaceutical opioids can be particularly attractive as a drug source because of their high purity and dependable dosage.
Abusers extract the pharmaceutical opioid, and other constituents, from the tablets. To do so, the tablets are crushed and often dissolved. The result may be further treated before it is ultimately injected or snorted to achieve, a “high”. This type of intranasal abuse is well documented.
The potential for abuse of pharmaceutical opioids is not a new problem. To combat the effects of opioid abuse, opioid antagonists have been used to block the euphoria associated with opioid abuse, and to induce withdrawal symptoms in addicts. One opioid antagonist used previously, and even now, is naloxone. Naloxone is a powerful antagonist of the opioid receptor. Naloxone is highly effective when taken parenterally, but poorly effective when taken orally because of its metabolism in the liver and, thus, has a high oral:parenteral potency ratio. When injected in humans, amounts as small as 0.2-0.4 mg can block the opioid receptors and prevent the user from experiencing the drug's effects, whether analgesia or mood alteration, euphoria. Because of the high oral:parenteral potency ratio (˜100) the antagonist action or oral doses of naloxone is much lower than the action of injections of naloxone. Because antagonists such as naloxone are less effective when taken orally, they have not been used to deter oral abuse and have been limited to deterring parenteral or intranasal abuse.
Recently however, a new form of abuse of opioid agonists has emerged involving oral abuse instead of abuse by injection or snorting. This practice has emerged largely because of the availability of high-opioid content controlled release (CR) formulations. “Chewing” involves crushing the opioid formulation and taking the entire contents, meant for 2 or more doses, at once. This practice releases all the opioid at once to generate a “high.” The crushing may take place in the mouth as suggested by the name, but also may occur by other means to make the opioid readily available including, crushing or dissolving the tablet prior to injection or administered intranasally.
Recently, high potency prescription opioid tablets containing large milligram doses of opioids have been introduced. These tablets are controlled release tablets and are designed to provide pain relief for 12 hours or more. Because the tablets have action over a long time period (12 hours instead of 4 hours for immediate release tablets), the tablets contain much higher quantities of opioid compounds. For potential abusers, these tablets are very attractive. Their high dosages make them a compact way to access large amounts of opioid. The fact that they are pharmaceuticals guarantees both the quality and quantity of drug in the tablet. Thus, the potential abuser knows he or she is obtaining a high purity drug in a known dosage. Prior oral opioid dosage formulations contained relatively low doses of opioid and were not generally targets for oral abuse. Their immediate release formulations release the opioid all at once, but with low amounts of opioid that would not be sufficient for oral abuse without putting several low dosage units together. In contrast, abusers have found that the new CR tablets contain large doses of opioid, which can be abused orally by chewing the tablets or crushing them to release all of the opioid at one time (immediate release). The present invention deters such oral abuse.
Oxycontin®, a controlled release oxycodone tablet from Purdue Pharma, is available in strengths as high as 160 mg oxycodone per tablet. The high opioid content makes these tablets especially attractive to abusers. Illegal trade in controlled release opioid tablets is becoming more prevalent. In order to obtain a euphoric effect (high) from such tablets, an abuser may crush the tablet and extract the opioid compound by dissolution for injection, or intranasal administration. Also, the abuser can achieve a euphoric effect from the drug by simply taking the drug orally, after chewing the tablet or grinding it to break the controlled release matrix and converting it to an immediate release product. Therefore, it would be desirable to have a formulation which would prevent the oral abuse of controlled release tablets if crushed to convert it to an immediate release product, without significantly affecting the analgesic action of opioid compounds in the intact controlled release tablet.
WO 01/58447 discloses pharmaceutical combinations of opioid agonists and antagonists in a controlled release matrix. The antagonist is present and released in amounts, over time, that attenuate or reduce the side effects of the opioid agonist, yet in amounts, insufficient to block the opioid effect. The preferred antagonist is Naltrexone, which is highly effective when administered orally or parenterally. The antagonist is released only in very small amounts, 100-1000 times less than the opioid. WO '447 is silent with respect to including an anti-abusive amount of antagonist in the dose to prevent abuse. The intravenous use of small amounts of naloxone, 0.25 or 1 μg kg−1hr−1, is also disclosed as having attenuating effects.
WO '447 does not present release rates for the antagonist in its CR formulation, but directs those skilled in the art to the Crain patents (U.S. Pat. Nos. 5,767,125; 5,580,876; 5,512,578; and 5,472,943). The Crain patents collectively disclose instant release formulations with “ultra-low” doses of certain antagonists to selectively block only the excitatory opioid receptors to attenuate opioid side effects, without blocking inhibitory receptors, which would lead to opioid blocking. These doses are on the order of pico-molar amounts. Crain '578 suggests that only naltrexone is useful in oral administration and that 1 μg doses are sufficient for attenuating opioid side effects by selectively blocking the excitatory opioid receptors and leaving the inhibitory opioid receptors free for receiving the opioid agonist (which may be administered in lower than normal doses with similar analgesic effect). The normal oral dose of naltrexone is about 50 mg versus “ultra low” does of 1 μg of naltrexone described in Crain '578 patent.
The prior art does not discuss controlled release formulation containing agonist and antagonist to deter abuse. Accordingly, there is a need for a composition that deters abuse in the high opioid-content controlled release formulation prevalent today.